target/linux/generic/backport-5.15/765-v5.17-06-net-next-net-dsa-setup-master-before-ports.patch

   1 From 11fd667dac315ea3f2469961f6d2869271a46cae Mon Sep 17 00:00:00 2001
   2 From: Vladimir Oltean <vladimir.oltean@nxp.com>
   3 Date: Thu, 6 Jan 2022 01:11:17 +0200
   4 Subject: [PATCH 6/6] net: dsa: setup master before ports
   5
   6 It is said that as soon as a network interface is registered, all its
   7 resources should have already been prepared, so that it is available for
   8 sending and receiving traffic. One of the resources needed by a DSA
   9 slave interface is the master.
  10
  11 dsa_tree_setup
  12 -> dsa_tree_setup_ports
  13    -> dsa_port_setup
  14       -> dsa_slave_create
  15          -> register_netdevice
  16 -> dsa_tree_setup_master
  17    -> dsa_master_setup
  18       -> sets up master->dsa_ptr, which enables reception
  19
  20 Therefore, there is a short period of time after register_netdevice()
  21 during which the master isn't prepared to pass traffic to the DSA layer
  22 (master->dsa_ptr is checked by eth_type_trans). Same thing during
  23 unregistration, there is a time frame in which packets might be missed.
  24
  25 Note that this change opens us to another race: dsa_master_find_slave()
  26 will get invoked potentially earlier than the slave creation, and later
  27 than the slave deletion. Since dp->slave starts off as a NULL pointer,
  28 the earlier calls aren't a problem, but the later calls are. To avoid
  29 use-after-free, we should zeroize dp->slave before calling
  30 dsa_slave_destroy().
  31
  32 In practice I cannot really test real life improvements brought by this
  33 change, since in my systems, netdevice creation races with PHY autoneg
  34 which takes a few seconds to complete, and that masks quite a few races.
  35 Effects might be noticeable in a setup with fixed links all the way to
  36 an external system.
  37
  38 Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
  39 Signed-off-by: David S. Miller <davem@davemloft.net>
  40 ---
  41  net/dsa/dsa2.c | 23 +++++++++++++----------
  42  1 file changed, 13 insertions(+), 10 deletions(-)
  43
  44 --- a/net/dsa/dsa2.c
  45 +++ b/net/dsa/dsa2.c
  46 @@ -545,6 +545,7 @@ static void dsa_port_teardown(struct dsa
  47         struct devlink_port *dlp = &dp->devlink_port;
  48         struct dsa_switch *ds = dp->ds;
  49         struct dsa_mac_addr *a, *tmp;
  50 +       struct net_device *slave;
  51
  52         if (!dp->setup)
  53                 return;
  54 @@ -566,9 +567,11 @@ static void dsa_port_teardown(struct dsa
  55                 dsa_port_link_unregister_of(dp);
  56                 break;
  57         case DSA_PORT_TYPE_USER:
  58 -               if (dp->slave) {
  59 -                       dsa_slave_destroy(dp->slave);
  60 +               slave = dp->slave;
  61 +
  62 +               if (slave) {
  63                         dp->slave = NULL;
  64 +                       dsa_slave_destroy(slave);
  65                 }
  66                 break;
  67         }
  68 @@ -1130,17 +1133,17 @@ static int dsa_tree_setup(struct dsa_swi
  69         if (err)
  70                 goto teardown_cpu_ports;
  71
  72 -       err = dsa_tree_setup_ports(dst);
  73 +       err = dsa_tree_setup_master(dst);
  74         if (err)
  75                 goto teardown_switches;
  76
  77 -       err = dsa_tree_setup_master(dst);
  78 +       err = dsa_tree_setup_ports(dst);
  79         if (err)
  80 -               goto teardown_ports;
  81 +               goto teardown_master;
  82
  83         err = dsa_tree_setup_lags(dst);
  84         if (err)
  85 -               goto teardown_master;
  86 +               goto teardown_ports;
  87
  88         dst->setup = true;
  89
  90 @@ -1148,10 +1151,10 @@ static int dsa_tree_setup(struct dsa_swi
  91
  92         return 0;
  93
  94 -teardown_master:
  95 -       dsa_tree_teardown_master(dst);
  96  teardown_ports:
  97         dsa_tree_teardown_ports(dst);
  98 +teardown_master:
  99 +       dsa_tree_teardown_master(dst);
 100  teardown_switches:
 101         dsa_tree_teardown_switches(dst);
 102  teardown_cpu_ports:
 103 @@ -1169,10 +1172,10 @@ static void dsa_tree_teardown(struct dsa
 104
 105         dsa_tree_teardown_lags(dst);
 106
 107 -       dsa_tree_teardown_master(dst);
 108 -
 109         dsa_tree_teardown_ports(dst);
 110
 111 +       dsa_tree_teardown_master(dst);
 112 +
 113         dsa_tree_teardown_switches(dst);
 114
 115         dsa_tree_teardown_cpu_ports(dst);